This invention relates to polycarbonamide-ester compositions, methods of forming creep resistant bonds between impervious materials and containers of composite construction. More particularly, this invention relates to containers of composite construction formed from a glass envelope of thin wall construction adhesively bonded with a hot melt adhesive, that is the product of the condensation of a dicarboxylic acid and an alkanolamine or a mixture of alkanolamine and diamine, to a plastic (preferably polyethylene) cup-like base designed for engaging the bottom or major portion of the glass envelope.
Ever since the introduction of the first commercial ethylene vinylacetate copolymers in the early 1960's, there has been an ever increasing demand for thermoplastic resins as adhesives by the packaging, and more recently by the product assembly industries. Of the several unique benefits hot melts have to offer over conventional bonding methods -- gap filling, speed, ability to bond impervious surfaces, reduced machinery cleanup time -- speed is the one characteristic most often emphasized, since this property alone can often make the difference between a successful and unsuccessful packaging line.
With the increasing shift in application of thermoplastic adhesives from the packaging to the product assembly industries, has come a shift in the emphasis with respect to the critical properties of thermoplastic adhesives. The tolerances for product assembly hot-melts are very much more critical than those for adhesives used in packaging where rather wide variations in application techniques, temperature, and other processing conditions can usually be tolerated without a great deal of difficulty.
The greater demands placed on thermoplastic adhesives by the product assembly industry has resulted in the development of a whole new class of so-called "high performance adhesives" based on polyesters, hydroxyvinyl resins, and polyamide polymers and copolymers. These more recently developed high performance thermoplastic adhesives, in addition to a number of the properties previously listed for conventional thermoplastic packaging adhesives, generally have increased tensile strength, greater flexibility, greater degree of wettability on a larger number of substrates, increased creep resistance, increased resistance to environmental conditions and sharper melting points.
Separate articles by J. R. Harrison and J. C. Hunt appearing in the October 1969 and August 1970 issues of "Adhesive Age" respectively, provide a relatively complete summary of the problems encountered in the use and selection of product assembly hot-melts and some of the advantages and limitations of specific adhesives currently in commercial use.
My invention is the discovery of certain relatively low molecular weight polycarbonamide-ester compositions which form highly creep resistant adhesive bonds between laminae generally acknowledged to be impervious to such materials. The strength of the adhesive bond is believed to be a function of the crystallinity of the adhesives which gradually increases with the aging of the adhesive. This unusually high degree of creep resistance of the adhesive when cured, coupled with the highly favorable flow characteristics of the polymer compositions at temperatures in the range of from about 125.degree. to 175.degree.C. make my adhesives very highly favorable as a product assembly hot melt.